That wire and boot by description shouldn't give you a shock on one and not the other so wire is highly the reason for the shock and it misfiring.
This is high voltage low amp power to jump the gap of a spark plug which it should prefer vs you unless somehow YOU are magnetically charged to be the easier path to ground at most the slightest fuzz feel while all hooked up.
It that plug is VERY hard (even new or same results with an old one that worked or swapped and same result) to accept the spark and the power then on to ground of engine block extra verifies it's the wire/boot combo.
Please understand this electricity - all really is seeking the least "resistant" way to ground intended to jump the gap of a spark plug in this case to make spark for ignition - doesn't matter now what fuel, any fuel at all should not jump spark out with any real force. It would be cancelling the spark unseen is not firing that plug to another place or may see it.
I still want you to use all caution getting shocked by this voltage! It's quite startling spark. Enough for some people to literally change a heart beat up to fatal results! Not common for fatal but has that power.
You may have seen emergency human beings when their heart stops emergency measures using electrical pads over person's heart "shock it" to start up again - I'm serious - about the same just targeted to do just that to save a life also could confuse your own body to stop your heart - so it is really a danger to avoid.
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I'll try to post a picture of the spark tester I was talking about or a link to the picture if possible. Handy tool that is just removable wires at each end to put in line (if room allows it at all) and will flash when spark travels thru it. Looks like this.........
Another try..........
Another similar one...........
Last one not as useful but same basic idea.
Here's the link to images found if nothing shows or pictures expire..........
https://www.google.com/...24.Q7OYFW6Jkhg#imgrc=_
This method you stand back and just watch while even just cranking an engine is enough if spark is present.
All this - you've found your trouble spot. It should be replaced with new again. Abusing these high voltage parts, just tugging on them to remove or problems handling them in manufacture, shipping or by person installing them could cause them to fail.
That tool in $US is listed as low as around $10. Price for EUROs and you location would probably convert to more.
New wires with paperwork intact should be warranted for FREE replacement.
I have to let you decide on how you acquire your own parts, in person at a parts store, on line purchases or what works best for you.
Good luck. That's your problem as best as I can determine from info provided,
Tom
(edited) only the last of three pics I posted shows for me. The link shows an entire assortment of spark testing tools to scroll thru. My view will allow and show where the picture came from - personal, a parts or tool store or anywhere a picture was posted that is allowed - that varies by location also........
